The present invention relates to a paint-coating brush to be mounted on an installation for the automatic application of a paint by means of a robot or the like.
Automatic installations have been used for the application of a paint such as a primer, varnish or adhesive, wherein a robot, manipulator or the like forms a part of the installation of this type. However, various problems are derived from the fact that the paint-coating brushes used in the conventional automatic installations are similar in construction to the paint-coating brushes used in manual painting.
FIG. 3 shows a conventional paint-coating brush B, which comprises a metal body 1, a plurality of piliform members 4, and a cylindrical sleeve 9 for fastening the piliform members 4 to the body 1.
The body 1 is provided with a threaded portion 6 on the butt side and a cylindrical spindle-shaped portion 8 on the muzzle side. The middle portion 7 disposed therebetween extends radially to provide a larger diameter than both end portions. The cylindrical spindle-shaped portion 8 is partially provided with a threaded portion 8a. The discharge of a paint is effected through an axial center bore 10 in the body 1. The sleeve 9 is provided with an annularly constricted portion 9b. The sleeve 9 is further provided with a tapped portion 9a to engage the threaded portion 8a of the body 1 so that the sleeve 9 may be fixedly mounted upon the body 1. The piliform members 4 are held in a cylindrical space 2 left between the spindle-shaped portion 8 of the body 1 and the sleeve 9.
The piliform members 4 consist of a comparatively soft material such as horsehair, hog hair or soft synthetic fibers. A plurality of piliform members 4 are bundled in a barrel-shaped manner on the outer surface of the spindle-shaped portion 8, against which the constricted portion 9b of the sleeve 9 presses the root portion 4a of the piliform members 4 so as to fixedly hold them in the cylindrical space 2 to dispose the remaining portion of the piliform members 4 in a position projecting outwardly of the opening of the sleeve 9 by about 20 to 35 millimeters.
In order to mount the paint-coating brush B on a paint-coating installation, the threaded portion 6 is threaded into a tapped hole 16 in the brush holder 15 of the paint-coating installation.
As might be apparent from FIG. 3, the above-described conventional paint-coating brush B has the disadvantage that the portion of the piliform members 4 projecting outwardly from the cylindrical space 2 is considerably long and consequently liable to be deformed.
In other words, the width of a paint coat undergoes changes, which are caused by the variation of pressure exerted by the piliform members 4 on the surface of an object to be coated with the paint. When this pressure fluctuates, especially when it abruptly increases, it causes the abrupt discharge and trickling of the paint with which the piliform members 4 have been soaked. Another disadvantage is derived from the fact that, because the projecting portion of the piliform members 4 is long, the paint comes in contact with air over a wide surface area. Consequently the paint is dried and hardened in the portions of the piliform members 4 which do not directly take part in the paint coating, i.e., in the middle portion of the piliform members 4 and in the portion close to the cylindrical space 2. Consequently, after the suspension of paint-coating operation, much time must be spent in washing the paint-coating brush B.
The above-described problems may be dissolved to some extent if short piliform members 4 are used so that the portion of the piliform members 4 projecting outwardly from the cylindrical space 2 may be shortened. However, the reduced overall length of the paint-coating brush B gives rise to another problem in that the movement of the brush holder 15 is occasionally hindered by the object to by coated with the paint. This is especially the case when a paint is to be applied to a stepped or narrow portion such as the window frame of an automobile. The paint-coating operation is rendered difficult or even impossible when the brush holder 15 or a pipeline connected thereto comes in contact with an edge or surface of such a stepped or narrow portion.
If bristles made of rigid resin such as nylon are used as the piliform members 4, they are free from liability to deformation, and the width of a paint coat is free from variation even if the pressure exerted by the piliform members 4 on the surface of an object to be coated with the paint undergoes variation. However, the fact that the bristles used as the piliform members 4 make point contact with the surface of the object gives rise to another problem in that uniform paint coating is made impossible, because a paint film with an uneven surface is formed. Still another problem is that the bristly piliform members 4 splash the paint at the time of paint coating, and the surroundings are stained with splashes.